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JCECE Engineering JCECE Engineering Solved Paper-2012

  • question_answer
    An engine approaches a hill with a constant speed. When it is at a distance of\[0.9\,\,km\], it blows a whistle, whose echo is heard by the driver after\[5\,\,s\]. If speed of sound in air is \[330\,\,m/s\], the speed of engine is

    A) \[10\,\,m/s\]                    

    B) \[20\,\,m/s\]

    C)  \[30\,\,m/s\]                   

    D)  \[40\,\,m/s\]

    Correct Answer: C

    Solution :

    If the speed of engine is v, the distance travelled by engine in 5 s will be 5v and hence the distance travelled by sound in reaching the hill and coming back to the moving driver                 \[=900+(900-5v)\]                 \[=1800-5v\] So, the time interval between original sound and its echo                 \[t=\frac{(1800-5v)}{330}=5\] \[\Rightarrow \]               \[v=30\,\,m/s\]


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